Investigation on the preparation and machinability of the B{sub}4C/BN nanocomposites by hot-pressing process

摘要

The machinable B{sub}4C/BN nanocomposites were fabricated by the hot-pressing process using the B{sub}4C/BN nanocomposite powders at 1850℃ for 1h under the pressure of 30MPa. The nanocomposite powders with the microstructure of micro-sized B{sub}4C particles coated with amorphous nano-sized BN particles were prepared by the chemical reaction of H{sub}3BO{sub}3 and CO(NH{sub}2){sub}2 on the surface of B{sub}4C particles at high temperature. Then the amorphous BN transformed into the hexagonal-BN (h-BN) after the hot-pressing process at 1850℃. The microstructure investigations of the B{sub}4C/BN nanocomposites sintered samples showed that the nano-sized h-BN particles were homogenously distributed within the matrix grains as well as at the matrix grains boundaries. With the increasing content of h-BN, the relative density of the B{sub}4C/BN nanocomposites decreased gradually. The fracture strength and fracture toughness of the B{sub}4C/BN nanocomposites decreased gradually, the fracture strength and fracture toughness of the B{sub}4C/BN nanocomposites with the h-BN content of 10wt.% and 20wt.% achieved high values. The Vickers hardness of the B{sub}4C/BN nanocomposites decreased remarkably with the increasing content of h-BN, while the drilling rates and machinability of the B{sub}4C/BN nanocomposites increased significantly. The B{sub}4C/BN nanocomposites with the h-BN content more than 20 wt.% exhibited excellent machinability.